net-im/t*: update Telegram Desktop: 4.1.1 -> 4.2.0

Remove experimental support for QT6. (*)

Changelog: https://github.com/telegramdesktop/tdesktop/compare/v4.1.1...v4.2.0

Discussed with: fluffy (*)

(cherry picked from commit f0fa5987b7a844886421f6c642b5a82731c4f7b6)